hewitt/lyons/suchocki/yeh conceptual integrated science

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley

Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated

Science

Chapter 6

HEAT


This lecture will help you understand:

• The Kinetic Theory of Matter• Temperature• Absolute Zero• What Is Heat?• Quantity of Heat• The Laws of Thermodynamics• Entropy• Specific Heat Capacity• Thermal Expansion• Expansion of Water• Heat Transfer: Conduction• Heat Transfer: Convection• Heat Transfer: Radiation• Emission of Radiant Energy• Absorption of Radiant Energy


The Kinetic Theory of Matter

Kinetic Theory of Matter:

Matter is made up of tiny particles (atoms or molecules) that are always in motion.

Thermal Energy:

The total energy (kinetic and potential) of the submicroscopic particles that make up a substance.


Temperature

Temperature

is defined as the measure of hotness or coldness of an object (degrees Celsius, or degrees Fahrenheit, or kelvins).

is related to the average translational kinetic energy per molecule in a substance.


Temperature

Thermometer

is an instrument that measures temperature by comparing the expansion and contraction of a liquid as it gains or loses thermal energy.

Infrared thermometer

measures temperature by the radiation a substance emits.


Temperature

Temperature has no upper limit.

Temperature of a substance is registered on a liquid-base thermometer when the substance has reached thermal equilibrium with the thermometer.


Temperature

Three different temperature scales differ in zero point and divisions:

• Celsius scale

freezing point of water: 0Cboiling point of water: 100Cdivision: 100 degree units


Temperature

• Fahrenheit scalefreezing point of water: 32 Fboiling point of water: 212 Fdivision: 180 degree units

• Kelvin scale (used in scientific research)freezing point of water: 273 Kboiling point of water: 373 Kdivision: same-size increments as Celsius scale


There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which will be the same for both?

A. Temperature.

B. Thermal energy.

C. Both of the above.

D. None of the above.

TemperatureCHECK YOUR NEIGHBOR


There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which will be the same for both?

A. Temperature.

B. Thermal energy.



Explanation:

Average kinetic energy of molecules is the same, which means temperature is the same for both.

TemperatureCHECK YOUR ANSWER


Absolute Zero

Absolute zero or zero K

is the lowest limit of temperature at –273C where molecules have lost all available kinetic energy. A substance cannot get any colder.


What Is Heat?

Heat

is defined as a flow of thermal energy due to a temperature difference.

The direction of heat flow is from a higher-temperature substance to a lower-temperature substance.


If a red hot thumbtack is immersed in warm water, the direction of heat flow will be from the

A. warm water to the red hot thumbtack.

B. red hot thumbtack to the warm water.

C. no heat flow.

D. not enough information.

What Is Heat?CHECK YOUR NEIGHBOR


If a red hot thumbtack is immersed in warm water, the direction of heat flow will be from the

A. warm water to the red hot thumbtack.

B. red hot thumbtack to the warm water.

C. no heat flow.


What Is Heat?CHECK YOUR ANSWER


Quantity of Heat

Heat is measured in units of energy—joules or calories.

calorieis defined as the amount of heat needed to raise the temperature of 1 gram of water by 1 Celsius degree.

4.18 joules = 1 calorie

so 4.18 joules of heat will change that temperature of 1 gram of water by 1 Celsius degree.


Quantity of Heat

Energy rating of food and fuel is measured by energy released when they are metabolized.

Kilocalorie:

Heat unit for labeling food

One kilocalorie or Calorie (with a capital C) is the heat needed to change the temperature of

1 kilogram of water by 1 degree Celsius.


The same quantity of heat is added to different amounts of water in two equal-size containers. The temperature of the smaller amount of water

A. decreases more.

B. increases more.

C. does not change.


Quantity of HeatCHECK YOUR NEIGHBOR


The same quantity of heat is added to different amounts of water in two equal-size containers. The temperature of the smaller amount of water

A. decreases more.

B. increases more.

C. does not change.


Quantity of HeatCHECK YOUR ANSWER


You heat a half-cup of tea and its temperature rises by 4C. How much will the temperature rise if you add the same amount of heat to a full cup of tea?

A. 0C.

B. 2C.

C. 4C.

D. 8C.

Quantity of HeatCHECK YOUR NEIGHBOR


You heat a half-cup of tea and its temperature rises by 4C. How much will the temperature rise if you add the same amount of heat to a full cup of tea?

A. 0C.

B. 2C.

C. 4C.

D. 8C.

Quantity of HeatCHECK YOUR ANSWER


The Laws of Thermodynamics

First Law of Thermodynamics:

Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred.

When thermal energy transfers as heat, it does so without net loss or gain.



Second Law of Thermodynamics:

Heat never spontaneously flows from a lower-temperature substance to a higher-temperature substance.

Heat can be made to flow the opposite way only when work is done on the system or by adding energy from another source.



Third Law of Thermodynamics:

No system can reach absolute zero.


When work is done on a system, compressing air in a tire pump, for example, the temperature of the system

A. increases.

B. decreases.

C. remains unchanged.

D. is no longer evident.

The Laws of ThermodynamicsCHECK YOUR NEIGHBOR


When work is done on a system, compressing air in a tire pump, for example, the temperature of the system

A. increases.

B. decreases.


D. is no longer evident.

Explanation:

In accord with the first law of thermodynamics, work input increases the energy of the system.

The Laws of ThermodynamicsCHECK YOUR ANSWER


Entropy

Entropyis a measure of the disorder of a system.

Whenever energy freely transforms from one form to another, the direction of transformation is toward a state of greater disorder and, therefore, toward one of greater entropy.

The greater the disorder the higher the entropy.


Entropy

Second law of thermodynamics — restatement:

Natural systems tend to disperse from concentrated and organized-energy states toward diffuse and disorganized states.

Energy tends to degrade and disperse with time.

The total amount of entropy in any system tends to increase with time.


Your room gets messier each week. In this case, the entropy of your room is

A. increasing.

B. decreasing.

C. hanging steady.

D. nonexistent.

EntropyCHECK YOUR NEIGHBOR


Your room gets messier each week. In this case, the entropy of your room is

A. increasing.

B. decreasing.

C. hanging steady.

D. nonexistent.

Comment:

If your room became more organized each week, then entropy would decrease in proportion to the effort expended.

EntropyCHECK YOUR ANSWER


Specific Heat Capacity

Specific heat capacity

is defined as the quantity of heat required to change the temperature of 1 unit mass of a substance by 1 degree Celsius.

• thermal inertia that indicates the resistance of a substance to a change in temperature.

• sometimes called specific heat.


Which has the higher specific heat, water or land?

A. Water.

B. Land.

C. Both of the above are the same.


Specific HeatCHECK YOUR NEIGHBOR


Which has the higher specific heat, water or land?

A. Water.

B. Land.

C. Both of the above are the same.


Explanation:

A substance with small temperature changes for large heat changes has a high specific heat capacity. Water takes much longer to heat up in the sunshine than does land. This difference is a major influence on climate.

Specific HeatCHECK YOUR ANSWER


Thermal Expansion

Thermal Expansion

When the temperature of a substance is increased, its particles jiggle faster and move farther apart.

All forms of matter generally expand when heated and contract when cooled.


When stringing telephone lines between poles in the summer, it is advisable to allow the lines to

A. sag.

B. be taut.

C. be close to the ground.

D. allow ample space for birds.

Thermal ExpansionCHECK YOUR NEIGHBOR


When stringing telephone lines between poles in the summer, it is advisable to allow the lines to

A. sag.

B. be taut.

C. be close to the ground.

D. allow ample space for birds.

Explanation:

Telephone lines are longer in a warmer summer and shorter in a cold winter. Hence, they sag more on hot summer days than in winter. If the lines are not strung with enough sag in summer, they might contract too much and snap during the winter—especially when carrying ice.

Thermal ExpansionCHECK YOUR ANSWER


Expansion of Water

Expansion of Water

When water becomes ice, it expands. Ice has open-structured crystals resulting from strong bonds at certain angles that increase its volume. This make ice less dense than water.


Expansion of Water

Water between 0C and 4C does not expand with temperature. As the temperature of 0 water rises, it contracts until it reaches 4C. Thereafter, it expands.

Water is at its smallest volume and greatest density at 4C. When 0C water freezes to become ice, however, it has its largest volume and lowest density.


Expansion of Water

Volume changes for a 1-gram sample of water.


When a sample of 0C water is heated, it first

A. expands.

B. contracts.



Expansion of WaterCHECK YOUR NEIGHBOR


When a sample of 0C water is heated, it first

A. expands.

B. contracts.



Explanation:

Water continues to contract until it reaches a temperature of 4C. With further increase in temperature beyond 4C, water then expands.

Expansion of WaterCHECK YOUR ANSWER


When a sample of 4C water is cooled, it

A. expands.

B. contracts.



Expansion of WaterCHECK YOUR NEIGHBOR


When a sample of 4C water is cooled, it

A. expands.

B. contracts.



Explanation:

Parts of the water will crystallize and occupy more space.

Expansion of WaterCHECK YOUR ANSWER


Heat Transfer

Processes of thermal energy transfer:• conduction• convection• radiation


Heat Transfer: Conduction

Conduction

occurs predominately in solids where the molecules remain in relatively restricted locations.



Example:

When one end of a solid is placed near a heat source, electrons and adjacent molecules gain kinetic energy and start to move faster and farther. They collide with neighboring molecules and transfer some of their kinetic energy to them. These molecules then interact with other neighboring molecules, and thermal energy is gradually transferred along the solid.



Good conductors:• composed of atoms with “loose” outer electrons• known as poor insulators• examples—all metals to varying degrees

Poor conductors:• delay the transfer of heat• known as good insulators• examples—wood, wool, straw, paper, cork, Styrofoam,

liquid, gases, air, or materials with trapped air



No insulator can totally prevent heat from getting through it.

An insulator reduces the rate at which heat penetrates.


If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand?

A. Yes.

B. In some cases, yes.

C. No.

D. In some cases, no.

Heat Transfer: ConductionCHECK YOUR NEIGHBOR


If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand?

A. Yes.

B. In some cases, yes.

C. No.

D. In some cases, no.

Explanation:

Cold does not flow from the ice to your hand. Heat flows from your hand to the ice. The metal is cold to your touch, because you are transferring heat to the metal.

Heat Transfer: ConductionCHECK YOUR ANSWER


Heat Transfer: Convection

Convection:• occurs in liquids and gases• involves the movement of warmer gases or

liquids to cooler surroundings

Two characteristics of convection:• the ability of flow—carrying thermal energy

with the fluid• the ability of warm fluid to rise in cooler

surroundings


Although warm air rises, why are mountaintops cold and snow covered, while the valleys below are relatively warm and green?

A. Warm air cools when rising.

B. There is a thick insulating blanket of air above valleys.



Heat Transfer: ConvectionCHECK YOUR NEIGHBOR


Although warm air rises, why are mountaintops cold and snow covered, while the valleys below are relatively warm and green?

A. Warm air cools when rising.

B. There is a thick insulating blanket of air above valleys.



Explanation:

Earth’s atmosphere acts as a blanket, which for one important thing, keeps Earth from freezing at nighttime.

Heat Transfer: ConvectionCHECK YOUR ANSWER


Heat Transfer: Radiation

Radiationis the process by which thermal energy is transferred by electromagnetic waves.

A thermal energy source such as the Sun converts some of its energy into electromagnetic waves. These waves carry energy, which converts back into thermal energy when absorbed by a receiver. The energy source radiates energy, and a receiver absorbs it.


Heat Transfer: Radiation

Wavelength of radiation is related to the frequency of vibration.

Low-frequency vibrations long wavesHigh-frequency vibrations short waves


Emission of Radiant Energy

Emission of Radiant Energy

All substances at any temperature above absolute zero emit radiant energy.

Average frequency ( ) of radiant energy is directly proportional to the absolute temperature T of the emitter:

T

f

f


If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be

A. lower.

B. higher.

C. unaffected.

D. none of the above.

Emission of Radiant EnergyCHECK YOUR NEIGHBOR


If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be

A. lower.

B. higher.

C. unaffected.

D. none of the above.

Explanation:

If a good absorber were not also a good emitter, there would be a net absorption of radiant energy, and the temperature of a good absorber would remain higher than the temperature of the surroundings. Nature is not so!

Emission of Radiant EnergyCHECK YOUR ANSWER


Absorption of Radiant Energy

Absorption of Radiant Energy:

The ability to absorb and radiate thermal energy is indicated by the color of the material.

Good absorbers and good emitters are dark in color.

Poor absorbers and poor emitters are reflective or light in color.



The surface of any material both absorbs and emits radiant energy.

When a surface absorbs more energy than it emits, it is a net absorber, and temperature rises.

When a surface emits more energy than it absorbs, it is a net emitter, and temperature falls.



Whether a surface is a net absorber or net emitter depends on whether its temperature is above or below that of its surroundings.

A surface hotter than its surroundings will be a net emitter and will cool.

A surface colder than its surroundings will be a net absorber and will warm.


Which melts faster in sunshine—dirty snow or clean snow?

A. Dirty snow.

B. Clean snow.



Absorption of Radiant EnergyCHECK YOUR NEIGHBOR


Which melts faster in sunshine—dirty snow or clean snow?

A. Dirty snow.

B. Clean snow.



Explanation:

Dirty snow absorbs more sunlight, whereas clean snow reflects more.

Absorption of Radiant EnergyCHECK YOUR ANSWER

hewitt/lyons/suchocki/yeh conceptual integrated science

Documents

pearson education

pearson addison wesleythere

thermal energy

molecular kinetic energy

kboiling point of water

fboiling point of water

cboiling point of water

total energy kinetic